A silicon ingot produced by the CZ method and the like has a cylindrical body portion and cone-shaped end portions (a top portion and a tail portion). In processing of the silicon ingot, these cone-shaped end portions are cut away to separate the cylindrical body portion, and the body portion is cut into a plurality of blocks as needed. The blocks are thereafter subjected to processing for obtaining a wafer.
An inner diameter slicer and an outer diameter slicer or the like have been frequently used for the case of the cutting processing of the cone-shaped end portions and the cutting processing of the body portion into a plurality of blocks. As the diameter of the wafer becomes larger in recent years, a band saw also has become to be frequently used.
Here, FIG. 6 shows an outline of a method for cutting into a block by using a conventional band saw cutting apparatus.
As shown in FIG. 6, a cutting table 105 for supporting the ingot 104 during cutting is arranged in the band saw cutting apparatus 101. The ingot 104 is horizontally placed on the cutting table 105 before cutting.
Moreover, in the band saw cutting apparatus 101, an endless-belt blade 102 is provided in a tensioned state between pulleys 103 and 103′, the blade which has a blade-abrasive-grain portion having abrasive grains of diamond adhered to an end portion of a thin blade base.
A position where the ingot 104 is placed is adjusted so that a cutting position of the ingot 104 corresponds to that of the blade 102.
The blade 102 is driven to rotate by rotating the pulleys 103 and 103′, and the ingot 104 is cut by relatively feeding the blade 102 from above to below.
In recent years, the blade that is made thinner has been used in the above-described band saw cutting apparatus in order to improve a product yield by reducing stock removal of the ingot during cutting.
As the cutting is repeated as described above, the abrasive grains are buried due to accumulating a cut powder on the blade-abrasive-grain portion, and the abrasive grains are worn by the cutting so that the cutting capacity of the blade is deteriorated. When the cutting is performed in such a state, there arises a problem that the blade 102 is displaced by an increase of cutting resistance to generate deflection of an edge of the blade 102 and that variation of cutting precision is generated, such as sori of the cut wafer.
Against this problem, there is disclosed a cutting method that is stated to enable a wafer having a uniform thickness to be stably obtained by detecting an increase and decrease of the cutting resistance during cutting from an increase and decrease of an electric power consumption of a first motor and by controlling an increase and decrease of a cutting rate of a second motor, which moves a blade in a cutting direction on the basis of the increase and decrease of the electric power consumption (See Patent Literature 1).